1. Field of the Invention
The present invention relates to a water-based ink for ink-jet recording and an ink cartridge.
2. Description of the Related Art
In a water-based ink for ink-jet recording, a self-dispersible pigment is used in some cases. The self-dispersible pigment can be obtained by performing a treatment such that at least one hydrophilic group such as phosphate group, carboxylic group, or sulfonate group (sulfonic acid group), or a salt thereof is bonded to the pigment. Since the self-dispersible pigment does not require any polymeric pigment dispersant, the self-dispersible pigment is capable of preventing the viscosity of the water-based ink from increasing. Further, a self-dispersible pigment, among the hydrophilic groups each bonded to the pigment, which is treated in particular with the phosphate group can obtain high optical density (OD value) as compared with a self-dispersible pigment which is treated with the carboxylic group or the sulfonate group.
On the other hand, the water-based ink using the self-dispersible pigment treated with the phosphate group has a problem such that the ink composition thereof generally does not have satisfactory re-dispersion property. In a case that the water-based ink which does not have the satisfactory re-dispersion property is once evaporated to dryness with resultant solid matter in the vicinity of an ink channel and/or nozzles of an ink-jet head, the following situation may possibly arise. That is, in a case that the water-based ink is tried to be jetted again and that the solid matter is newly brought in contact with the water-based ink, the solid matter is not dissolved and dispersed. Thus, it is feared that any trouble occurs in jetting stability.
In view of the above situation, an object of the present teaching is to provide a water-based ink for ink-jet recording which includes a self-dispersible pigment, which has excellent re-dispersion property, and which can obtain relatively-high optical density (OD value).